Structure and formation method of semiconductor device with fin structures

ABSTRACT

A structure and a method of a semiconductor device structure are provided. The method includes forming a first fin structure, a second fin structure, and a third fin structure over a semiconductor substrate. The method includes forming first spacer elements over sidewalls of the first fin structure and the second fin structure and partially removing the first fin structure and the second fin structure. The method includes forming second spacer elements over sidewalls of the third fin structure and partially removing the third fin structure. The second spacer element is taller than the first spacer element. The method includes epitaxially growing a semiconductor material over the first fin structure, the second fin structure, and the third fin structure such that a merged semiconductor element is formed on the first fin structure and the second fin structure, and an isolated semiconductor element is formed on the third fin structure.

PRIORITY CLAIM AND CROSS-REFERENCE

This Application claims the benefit of U.S. Provisional Application No.62/589,081, filed on Nov. 21, 2017, the entirety of which isincorporated by reference herein.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. Technological advances in IC materials and design have producedgenerations of ICs. Each generation has smaller and more complexcircuits than the previous generation.

In the course of IC evolution, functional density (i.e., the number ofinterconnected devices per chip area) has generally increased whilegeometric size (i.e., the smallest component (or line) that can becreated using a fabrication process) has decreased. This scaling-downprocess generally provides benefits by increasing production efficiencyand lowering associated costs.

However, these advances have increased the complexity of processing andmanufacturing ICs. Since feature sizes continue to decrease, fabricationprocesses continue to become more difficult to perform. Therefore, it isa challenge to form reliable semiconductor devices at smaller andsmaller sizes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It shouldbe noted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a top view of a semiconductor device structure, in accordancewith some embodiments.

FIG. 2 is a perspective view of a stage of a process for forming asemiconductor device structure, in accordance with some embodiments.

FIGS. 3A-3J are cross-sectional views of various stages of a process forforming a semiconductor device structure, in accordance with someembodiments.

FIGS. 4A-4E are cross-sectional views of various stages of a process forforming a semiconductor device structure, in accordance with someembodiments.

FIG. 5 is a cross-sectional view of a semiconductor device structure, inaccordance with some embodiments.

FIG. 6 is a cross-sectional view of a semiconductor device structure, inaccordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Some embodiments of the disclosure are described. Additional operationscan be provided before, during, and/or after the stages described inthese embodiments. Some of the stages that are described can be replacedor eliminated for different embodiments. Additional features can beadded to the semiconductor device structure. Some of the featuresdescribed below can be replaced or eliminated for different embodiments.Although some embodiments are discussed with operations performed in aparticular order, these operations may be performed in another logicalorder.

Embodiments of the disclosure may relate to FinFET structure havingfins. The fins may be patterned by any suitable method. For example, thefins may be patterned using one or more photolithography processes,including double-patterning or multi-patterning processes. Generally,double-patterning or multi-patterning processes combine photolithographyand self-aligned processes, allowing patterns to be created that have,for example, pitches smaller than what is otherwise obtainable using asingle, direct photolithography process. For example, in someembodiments, a sacrificial layer is formed over a substrate andpatterned using a photolithography process. Spacers are formed alongsidethe patterned sacrificial layer using a self-aligned process. Thesacrificial layer is then removed, and the remaining spacers may then beused to pattern the fins. However, the fins may be formed using one ormore other applicable processes.

FIG. 1 is a top view of a semiconductor device structure, in accordancewith some embodiments. In some embodiments, the semiconductor devicestructure includes a first region 10 and a second region 20. The secondregion 20 may be a cell region that includes multiple memory devices. Insome embodiments, the second region 20 includes multiple staticrandom-access memory (SRAM) devices. The first region 10 may be a pickupregion that includes multiple devices. These devices may be inelectrical communication with the memory devices in the second region20. The first region 10 and the second region 20 may each includemultiple fin field-effect transistors (FinFETs).

FIG. 2 is a perspective view of a stage of a process for forming asemiconductor device structure, in accordance with some embodiments. Insome embodiments, FIG. 2 shows one of the FinFETs in the first region 10and one of the FinFETs in the second region.

FIGS. 3A-3J are cross-sectional views of various stages of a process forforming a semiconductor device structure, in accordance with someembodiments. As shown in FIG. 3A, a semiconductor substrate 100 isreceived or provided. Portions of the first region 10 and the secondregion 20 are shown. In some embodiments, the first region 10 shown inFIG. 3A corresponds to a cross-sectional view taken along the line I-Iof FIG. 2, and the second region 20 shown in FIG. 3A corresponds to across-sectional view taken along the line J-J of FIG. 2.

In some embodiments, the semiconductor substrate 100 is a bulksemiconductor substrate, such as a semiconductor wafer. For example, thesemiconductor substrate 100 includes silicon or other elementarysemiconductor materials such as germanium. The semiconductor substrate100 may be un-doped or doped (e.g., p-type, n-type, or a combinationthereof). In some other embodiments, the semiconductor substrate 100includes a compound semiconductor. The compound semiconductor mayinclude silicon carbide, gallium arsenide, indium arsenide, indiumphosphide, one or more other suitable compound semiconductors, or acombination thereof. In some embodiments, the semiconductor substrate100 is an active layer of a semiconductor-on-insulator (SOI) substrate.The SOI substrate may be fabricated using a separation by implantationof oxygen (SIMOX) process, a wafer bonding process, another applicablemethod, or a combination thereof. In some other embodiments, thesemiconductor substrate 100 includes a multi-layered structure. Forexample, the semiconductor substrate 100 includes a silicon-germaniumlayer formed on a bulk silicon layer.

As shown in FIG. 3A and FIG. 2, multiple recesses (or trenches) areformed in the semiconductor substrate 100, in accordance with someembodiments. As a result, multiple fin structures including finstructures 102A, 102B, 102C, and 102D are formed or defined between therecesses. In some embodiments, one or more photolithography and etchingprocesses are used to form the recesses. In some embodiments, the finstructures 102A, 102B, 102C, and 102D are in direct contact with thesemiconductor substrate 100. As shown in FIG. 3A, each of the finstructures 102A, 102B, 102C and 102D has a height H₁. The height H₁ maybe in a range from about 50 nm to about 60 nm.

However, embodiments of the disclosure have many variations and/ormodifications. In some other embodiments, the fin structures 102A, 102B,102C, and 102D are not in direct contact with the semiconductorsubstrate 100. One or more other material layers may be formed betweenthe semiconductor substrate 100 and the fin structures 102A, 102B, 102C,and 102D. For example, a dielectric layer may be formed therebetween.

As shown in FIG. 3A and FIG. 2, isolation features 104 are formed in therecesses to surround lower portions of the fin structures 102A, 102B,102C, and 102D, in accordance with some embodiments. The isolationfeatures 104 are used to define and electrically isolate various deviceelements formed in and/or over the semiconductor substrate 100. In someembodiments, the isolation features 104 include shallow trench isolation(STI) features, local oxidation of silicon (LOCOS) features, anothersuitable isolation feature, or a combination thereof.

In some embodiments, each of the isolation features 104 has amulti-layer structure. In some embodiments, the isolation features 104are made of a dielectric material. The dielectric material may includesilicon oxide, silicon nitride, silicon oxynitride, fluoride-dopedsilicate glass (FSG), low-K dielectric material, one or more othersuitable materials, or a combination thereof. In some embodiments, anSTI liner (not shown) is formed to reduce crystalline defects at theinterface between the semiconductor substrate 100 and the isolationfeatures 104. Similarly, the STI liner may also be used to reducecrystalline defects at the interface between the isolation features 104and the fin structures 102A, 102B, 102C, and 102D.

In some embodiments, a dielectric material layer is deposited over thesemiconductor substrate 100. The dielectric material layer covers thefin structures 102A, 102B, 102C, and 102D and fills the recesses betweenthe fin structures. In some embodiments, the dielectric material layeris deposited using a chemical vapor deposition (CVD) process, an atomiclayer deposition (ALD) process, a physical vapor deposition (PVD)process, a spin-on process, one or more other applicable processes, or acombination thereof. In some embodiments, a planarization process isused to thin down the dielectric material layer until the fin structures102A, 102B, 102C, and 102D or hard mask elements defining the finstructures are exposed. The planarization process may include a chemicalmechanical polishing (CMP) process, a grinding process, a dry polishingprocess, an etching process, one or more other applicable processes, ora combination thereof. Afterwards, the dielectric material layer isetched back such that the fin structures 102A, 102B, 102C, and 102Dprotrude from the top surface of the remaining dielectric material layerafter the etching process. As a result, the remaining portions of thedielectric material layer form the isolation features 104, as shown inFIG. 3A and FIG. 2.

Afterwards, multiple gate stacks are formed over the semiconductorsubstrate 100 to partially cover the fin structures 102A, 102B, 102C,and 102D, as shown in FIG. 2 in accordance with some embodiments. Asshown in FIG. 2, a first gate stack and a second gate stack includinggate electrodes 108A and 108B and a gate dielectric layer 106 areformed. The first gate stack partially covers the fin structures 102Aand 102B. The second gate stack partially covers the fin structures 102Cand 102D.

In some embodiments, a gate dielectric layer 106 and a gate electrodelayer are deposited over the isolation features 104 and the finstructures 102A, 102B, 102C, and 102D. In some embodiments, the gatedielectric layer 106 is made of or includes silicon oxide, siliconnitride, silicon oxynitride, dielectric material with a high dielectricconstant (high-K), one or more other suitable dielectric materials, or acombination thereof. Examples of high-K dielectric materials includehafnium oxide, zirconium oxide, aluminum oxide, hafnium dioxide-aluminaalloy, hafnium silicon oxide, hafnium silicon oxynitride, hafniumtantalum oxide, hafnium titanium oxide, hafnium zirconium oxide, one ormore other suitable high-K materials, or a combination thereof. In someembodiments, the gate dielectric layer 106 is a dummy gate dielectriclayer 106 which will be removed subsequently. The dummy gate dielectriclayer 106 is, for example, a silicon oxide layer.

In some embodiments, the gate dielectric layer 106 is deposited using achemical vapor deposition (CVD) process, an atomic layer deposition(ALD) process, a thermal oxidation process, a physical vapor deposition(PVD) process, one or more other applicable processes, or a combinationthereof.

In some embodiments, the gate electrode layer is a dummy gate electrodelayer and is made of or includes a semiconductor material such aspolysilicon. For example, the dummy gate electrode layer is depositedusing a CVD process or another applicable process.

Afterwards, a patterned hard mask element 110 is formed over the gateelectrode layer, as shown in FIG. 2 in accordance with some embodiments.The patterned hard mask element 110 is used to pattern the gateelectrode layer and the gate dielectric layer 106 into one or more gatestacks. Afterwards, the gate electrode layer and the gate dielectriclayer 106 are etched with the patterned hard mask element 110 as anetching mask to form the gate stacks, as shown in FIG. 2 in accordancewith some embodiments.

As shown in FIG. 3B, a spacer layer 112 is deposited over the finstructures 102A, 102B, 102C, and 102D, in accordance with someembodiments. The spacer layer 112 extends over the isolation features102. The spacer layer 112 also extends on sidewalls and top surfaces ofthe fin structures 102A, 102B, 102C, and 102D. In some embodiments, thespacer layer 112 extends on sidewalls and top surfaces of the gatestacks. The spacer layer 112 may be made of or include one or moredielectric materials. Examples of the dielectric material(s) includesilicon nitride, silicon oxynitride, silicon carbide, silicon oxide,silicon oxycarbide, one or more other suitable materials, or acombination thereof. The spacer layer 112 may be deposited using a CVDprocess, an ALD process, a PVD process, one or more other applicableprocesses, or a combination thereof.

As shown in FIG. 3C, a mask element 114 is formed to cover a part of thespacer layer 112 over the fin structures 102A and 102B, in accordancewith some embodiments. The mask element 114 is used as an etching maskduring a subsequent etching process for forming spacer elements onsidewalls of the fin structures 102C and 102D. In some embodiments, themask element 114 is made of a different material than that of the spacerlayer 112. In some embodiments, a patterned photoresist layer is used todefine the mask element 114. In some other embodiments, the mask element114 includes a patterned photoresist layer.

In some embodiments, the mask element 114 is a blanket layer coveringthe fin structures 102A and 102B. However, many variations and/ormodifications can be made to embodiments of the disclosure. In someother embodiments, the mask element 114 is a conformal layer coveringthe sidewalls and top surfaces of the fin structures 102A and 102B.

Afterwards, the spacer layer 112 not covered by the mask element 114 ispartially removed, as shown in FIG. 3C in accordance with someembodiments. As a result, some remaining portions of the spacer layer112 form spacer elements 116 over the sidewalls of the fin structures102C and 102D. Some other remaining portions of the spacer layer 112 mayform gate spacer elements over the sidewalls of the gate stack notcovered by the mask element 114. For example, gate spacer elements areformed on sidewalls of the gate electrode 108B. In some embodiments, anetching process is used to partially remove the spacer layer 112 so asto form the spacer elements 116. The etching process may be ananisotropic etching process.

In some embodiments, the etching process for forming the spacer elements116 is a plasma-involved dry etching process. A mixture of gases may beused to generate the plasma. The mixture of gases may include CH₄, HBr,O₂, one or more other suitable gases, or a combination thereof.

As shown in FIG. 3D, the fin structures 102C and 102D are partiallyremoved, in accordance with some embodiments. As a result, recessed (orthinned) fin structures 102C′ and 102D′ are formed. In some embodiments,an etching process is used to partially remove the fin structures 102Cand 102D. In some embodiments, the etching process for partiallyremoving the fin structures 102C and 102D is a plasma-involved dryetching process. A mixture of gases may be used to generate the plasma.The mixture of gases may include HBr, O₂, one or more other suitablegases, or a combination thereof.

The etchant used in the etching process may also partially or slightlyremove the spacer elements 116. Therefore, spacer elements 116′ that arelower than the spacer elements 116 are formed, as shown in FIG. 3D inaccordance with some embodiments. In some embodiments, recesses 118surrounded by the spacer elements 116′ are formed on the fin structures102C′ and 102D′.

As shown in FIG. 3E, the mask element 114 is removed, and a mask element120 is formed to cover the spacer elements 116′ and the fin structures102C′ and 102D′, in accordance with some embodiments. A portion of thespacer layer 112 covering the fin structures 102A and 102B is exposedwithout being covered by the mask element 120, as shown in FIG. 3E. Thematerial and formation method of the mask element 120 may be the same asor similar to those of the mask element 114.

As shown in FIG. 3F, the spacer layer 112 not covered by the maskelement 120 is partially removed, in accordance with some embodiments.As a result, some remaining portions of the spacer layer 112 form spacerelements 121 over the sidewalls of the fin structures 102A and 102B. Insome embodiments, each of the spacer elements 121 is shorter than eachof the spacer elements 116′. Some other remaining portions of the spacerlayer 112 may form spacer elements over the sidewalls of the gate stacknot covered by the mask element 120. For example, spacer elements areformed on sidewalls of the gate electrode 108A in FIG. 2. In someembodiments, an etching process is used to partially remove the spacerlayer 112 so as to form the spacer elements 121. The etching process maybe an anisotropic etching process.

In some embodiments, the etching process used for forming the spacerelements 121 may be the same as or similar to that used for forming thespacer elements 116 as illustrated in FIG. 3C. In some embodiments, theetching time for forming the spacer elements 121 is longer than that forforming the spacer elements 116. As a result, each of the spacerelements 121 is shorter than each of the spacer elements 116 or 116′, asshown in FIG. 3F. The etching time for forming the spacer elements 121may in a range from about 30 seconds to about 60 seconds. The etchingtime for forming the spacer elements 116 may in a range from about 20seconds to about 40 seconds.

As shown in FIG. 3G, the fin structures 102A and 102B are partiallyremoved, in accordance with some embodiments. As a result, recessed (orthinned) fin structures 102C′ and 102D′ are formed. In some embodiments,an etching process is used to partially remove the fin structures 102Aand 102B. The etchant used in the etching process may also partially orslightly remove the spacer elements 121. Therefore, spacer elements 121′that are lower than the spacer elements 121 are formed, as shown in FIG.3G in accordance with some embodiments. In some embodiments, recesses124 surrounded by the spacer elements 121′ are formed on the finstructures 102A′ and 102B′.

In some embodiments, the etching process used for partially removing thefin structures 102A and 102B may be the same as or similar to that usedfor partially removing the fin structures 102C and 102D as illustratedin FIGS. 3C-3D. In some embodiments, the etching time for partiallyremoving the fin structures 102A and 102B is longer than that forpartially removing the fin structures 102C and 102D. As a result, eachof the fin structures 102A′ and 102B′ is shorter than each of the finstructures 102C′ and 102D′, as shown in FIG. 3G. The etching time forforming the (recessed) fin structures 102A′ and 102B′ may be in a rangefrom about 30 seconds to about 60 seconds. The etching time for formingthe (recessed) fin structures 102C′ and 102D′ may be in a range fromabout 20 seconds to about 50 seconds.

Many variations and/or modifications can be made to embodiments of thedisclosure. In some other embodiments, the spacer elements 121 arecompletely removed during or after the formation of the fin structures102A′ and 102B′. In these cases, the spacer elements 121′ are notformed.

As shown in FIG. 3H, the mask element 120 is removed, in accordance withsome embodiments. As a result, the fin structures 102A′, 102B′, 102C′and 102D′ and the spacer elements 121′ and 116′ are exposed. In someembodiments, each of the fin structures 102C′ and 102D′ is taller thaneach of the fin structures 102A′ and 102B′. The top surface of the finstructures 102C′ or 102D′ is higher than the top surfaces of the finstructures 102A′ and 102B′, as shown in FIG. 3H.

In some embodiments, the top surfaces of the fin structures 102A′ and102B′ are lower than the top surface of the isolation features 104 by aheight h₁, as shown in FIG. 3H. The height h₁ may be in a range fromabout 1 nm to about 10 nm. In some embodiments, the top surface of thefin structures 102C′ and 102D′ are higher than the top surface of theisolation features 104 by a height h₂, as shown in FIG. 3H. The heighth₂ may be in a range from about 5 nm to about 15 nm.

In some embodiments, each of the spacer elements 116′ is taller thaneach of the spacer elements 121′. In some embodiments, one or each ofthe spacer elements 121′ has a height h₃, and one or each of the spacerelements 116′ has a height h₄, as shown in FIG. 3H. The height h₃ may bein a range from about 2 nm to about 15 nm. In some embodiments, thespacer elements 121′ are completely removed. In these cases, the heighth₃ is zero. The height h₄ may be in a range from about 10 nm to about 30nm. In some embodiments, a height ratio (h₃/h₄) of the height h₃ to theheight h₄ is in a range from about 0 to about 0.5. In some cases, if theheight ratio (h₃/h₄) is greater than about 0.5, the height h₃ may be toohigh, which might negatively affect a subsequent epitaxial growth of amerged semiconductor structure.

As shown in FIG. 31, one or more semiconductor materials are epitaxiallygrown over the fin structures 102A′, 102B′, 102C′, and 102D′, inaccordance with some embodiments. As a result, a merged semiconductorelement 130 is formed on the fin structures 102A′ and 102B′. The mergedsemiconductor element 130 has a first portion connecting the finstructure 102A′ and a second portion connecting the fin structure 102B′.Isolated semiconductor elements 132 are formed on the fin structures102C′ and 102D′, respectively. The merged semiconductor element 130 mayserve as a source/drain structure of a transistor. The isolatedsemiconductor elements 132 which are separated from each other by adistance may serve as source/drain structures of different transistors.In some embodiments, the merged semiconductor element 130 and theisolated semiconductor elements 132 are simultaneously formed.

In some embodiments, the merged semiconductor element 130 is wider andtaller than each of the isolated semiconductor elements 132, as shown inFIG. 31. As shown in FIG. 31, the merged semiconductor element 130 has awidth W₁, and each of the isolated semiconductor elements 132 has awidth W₂. The width W_(i) is greater than the width W₂. The mergedsemiconductor element 130 thus has a greater surface area than theisolated semiconductor element 132. Therefore, resistance between themerged semiconductor element 130 and a conductive contact formed thereonmay be reduced. The electrical properties of the semiconductor devicestructure are significantly improved.

As shown in FIG. 31, the merged semiconductor element 130 has a heightH₂, and each of the isolated semiconductor elements 132 has a height H₃.In some embodiments, the height H₂ is greater than the height H₃. Insome embodiments, each of the fin structures 102A, 102B, 102C, and 102Doriginally has a height H₁, as shown in FIG. 3A. In some embodiments,the height H₂ is greater than the height H₁. In some embodiments, theheight H₃ is smaller than the height H₁. In some other embodiments, theheight H₃ is substantially equal to the height H₁.

The height H₂ of the merged semiconductor element 130 may be in a rangefrom about 55 nm to about 70 nm. The height H₃ of the isolatedsemiconductor element 132 may be in a range from about 40 nm to about 60nm. In some embodiments, the height ratio (H₃/H₂) of the height H₃ toheight H₂ may be in a range from about 0.7 to about 0.9. In some cases,if the height ratio (H₃/H₂) is smaller than about 0.7, the heightdifferent between the merged semiconductor element 130 and the isolatedsemiconductor element 132 may be too much. A subsequent formation ofconductive contacts might be negatively affected. In some other cases,if the height ratio (H₃/H₂) is greater than about 0.9, the isolatedsemiconductor element 132 might come in contact with a neighboringisolated semiconductor element 132 and be grown to be a mergedsemiconductor element. As a result, the devices in the second region 20might not be able to provide the designed functions.

In some embodiments, the growth of the merged semiconductor element 130and the isolated semiconductor elements 132 are performedsimultaneously. In some other embodiments, the growth of the mergedsemiconductor element 130 and the isolated semiconductor elements 132are performed separately in different processes.

In some embodiments, because each of the spacer elements 121′ has asmall height, the epitaxial growth of the semiconductor material on thefin structures 102A′ and 102B′ is less confined than the epitaxialgrowth of the semiconductor material on the fin structures 102C′ and102D′ surrounded by the spacer elements 116′ having a greater height.Therefore, the grown semiconductor material on the fin structures 102A′and 102B′ may reach each other and together form the mergedsemiconductor element 130. The grown semiconductor material on the finstructures 102C′ and 102D′ is confined due to the spacer elements 116′with a greater height than the spacer elements 121′. Therefore, thegrown semiconductor material on the fin structures 102C′ and 102D′ doesnot reach each other. As a result, the isolated semiconductor elements132 on the fin structures 102C′ and 102D′ are prevented from reachingeach other. In some embodiments, the isolated semiconductor elements 132are designed to be separated from each other for some design purposes.

In some embodiments, the merged semiconductor element 130 and theisolated semiconductor elements 132 are made of a p-type semiconductormaterial. For example, the merged semiconductor element 130 and theisolated semiconductor elements 132 may include epitaxially grownsilicon germanium. In some other embodiments, the merged semiconductorelement 130 and the isolated semiconductor elements 132 are made of ann-type semiconductor material. The merged semiconductor element 130 andthe isolated semiconductor elements 132 may include epitaxially grownsilicon, epitaxially grown silicon carbide (SiC), epitaxially grownsilicon phosphide (SiP), or another suitable epitaxially grownsemiconductor material.

In some embodiments, the merged semiconductor element 130 and theisolated semiconductor elements 132 are formed using a selective epitaxygrowth (SEG) process, a CVD process (e.g., a vapor-phase epitaxy (VPE)process, a low pressure chemical vapor deposition (LPCVD) process,and/or an ultra-high vacuum CVD (UHV-CVD) process), a molecular beamepitaxy process, one or more other applicable processes, or acombination thereof. The formation process of the merged semiconductorelement 130 and the isolated semiconductor elements 132 may use gaseousand/or liquid precursors.

In some embodiments, both the merged semiconductor element 130 and theisolated semiconductor elements 132 are grown in the same processchamber. The merged semiconductor element 130 and the isolatedsemiconductor elements 132 may be formed using an in-situ epitaxialgrowth process.

Many variations and/or modifications can be made to embodiments of thedisclosure. In some other embodiments, the merged semiconductor element130 and the isolated semiconductor elements 132 are grown separately indifferent process chambers.

In some embodiments, the merged semiconductor element 130 and theisolated semiconductor elements 132 include dopants. For example, themerged semiconductor element 130 and the isolated semiconductor elements132 are p-type doped, and the dopants may include boron, gallium, or acombination thereof. In some embodiments, multiple implantationprocesses are performed to dope the merged semiconductor element 130 andthe isolated semiconductor elements 132. In some embodiments, the mergedsemiconductor element 130 and the isolated semiconductor elements 132are not doped during the growth of the merged semiconductor element 130and the isolated semiconductor elements 132. After the epitaxial growth,the merged semiconductor element 130 and the isolated semiconductorelements 132 are doped in a subsequent process.

In some embodiments, the doping is achieved using an ion implantationprocess, a plasma immersion ion implantation process, a gas and/or solidsource diffusion process, one or more other applicable processes, or acombination thereof. In some embodiments, the merged semiconductorelement 130 and the isolated semiconductor elements 132 are furtherexposed to one or more annealing processes to activate the dopants. Forexample, a rapid thermal annealing process is used.

In some embodiments, the merged semiconductor element 130 and theisolated semiconductor elements 132 are doped in-situ during the growthof the merged semiconductor element 130 and the isolated semiconductorelements 132. In some embodiments, a first semiconductor-containing gasis introduced into the process chamber to epitaxially grow innerportions 126A of the merged semiconductor element 130 and inner portions126B of the isolated semiconductor elements 132. Afterwards, a secondsemiconductor-containing gas is introduced into the same process chamberto epitaxially grow an outer portion 128B of the merged semiconductorelement 130 and outer portions 128B of the isolated semiconductorelements 132. The outer portion 128A surrounds the inner portion 126A,and the outer portion 128B surrounds the inner portion 126B, as shown inFIG. 31.

In some embodiments, the first semiconductor-containing gas and thesecond semiconductor-containing gas each contains silicon and germanium.In some embodiments, one or both of the first semiconductor-containinggas and the second semiconductor-containing gas contains dopants. Insome embodiments, the second semiconductor-containing gas has adifferent dopant concentration than that of the firstsemiconductor-containing gas. In some embodiments, the secondsemiconductor-containing gas has a greater dopant concentration thanthat of the first semiconductor-containing gas.

In some embodiments, the outer portion 128B of each of the isolatedsemiconductor elements 132 has a greater dopant concentration than thatof the inner portion 126B. In some embodiments, the outer portion 128Aof the merged semiconductor element 130 has a greater dopantconcentration than that of the inner portion 126A. In some embodiments,the dopant concentration of the inner portion 126A is the same as thatof the inner portion 126B. In some embodiments, the dopant concentrationof the outer portion 128A is the same as that of the outer portion 128B.The inner portion 126A and/or the inner portion 126B may have a dopantconcentration that is in a range from about 10²⁰ atoms/cm³ to about 10²¹atoms/cm³. The outer portion 128A and/or 128B may have a dopantconcentration that is in a range from about 10²¹ atoms/cm³ to about 10²²atoms/cm³.

In some embodiments, during the growth of the merged semiconductorelement 130, the grown semiconductor material on the neighboringsemiconductor fins reach each other and provide a plane for thesemiconductor material continue to grow at a higher speed than that isgrown on the inner portion 126B of the isolated semiconductor element132. As a result, the outer portion 128A of the merged semiconductorelement 130 is larger than the outer portion 128B of the isolatedsemiconductor element 132. The merged semiconductor element 130 has agreater volume ratio of the outer portion to the inner portion than thatof the isolated semiconductor element 132. The outer portion 128Aoccupies a first fraction of the merged semiconductor element 130. Theouter portion 128B occupies a second fraction of the isolatedsemiconductor element 132. In some embodiments, the first fraction isgreater than the second fraction. In some embodiments, the outer portion128A is larger than each of the inner portions 126A of the mergedsemiconductor element 130. In some embodiments, the outer portion 128Bis smaller than the inner portion 126B of the isolated semiconductorelement 132. As mentioned above, the outer portion has a greater dopantconcentration than the inner portion. Therefore, the mergedsemiconductor element 130 that has a larger outer portion may have ahigher conductivity than the isolated semiconductor element 132.

As shown in FIG. 3J, a surrounding portion 129A of the mergedsemiconductor element 130 and surrounding portions 129B of the isolatedsemiconductor elements 132 are formed, in accordance with someembodiments. In some embodiments, the surrounding portions 129A and 129Bsurround the outer portions 128A and 128B, respectively. In someembodiments, the surrounding portion 129A has a lower dopantconcentration than that of the outer portion 128A. In some embodiments,the surrounding portion 129B has a lower dopant concentration than thatof the outer portion 128B. In some embodiments, the surrounding portions129A and 129B are simultaneously formed. In some embodiments, thesurrounding portions 129A and 129B are in-situ formed in the sameprocess chamber for forming the outer portions 128A and 128B.

In the embodiments illustrated in FIGS. 3A-3J, two mask elementsincluding the mask elements 114 and 120 are used for forming the spacerelements 121′ and 116′. However, many variations and/or modificationscan be made to embodiments of the disclosure. In some other embodiments,only one mask element is used for forming spacer elements with differentheights.

FIGS. 4A-4E are cross-sectional views of various stages of a process forforming a semiconductor device structure, in accordance with someembodiments. As shown in FIG. 4A, a structure the same as or similar tothat shown in FIG. 3B is formed or received, in accordance with someembodiments.

Afterwards, etching processes the same as or similar to the etchingprocesses illustrated in FIGS. 3C-3D are performed without the formationof the mask element 114, as shown in FIG. 4B in accordance with someembodiments. As a result, spacer elements 116′ are formed, and the finstructures are partially removed to form the fin structures 102A″,102B″, 102C′ and 102D′, as shown in FIG. 4B. The spacer elements 116′extend along the sidewalls of the fin structures 102A″, 102B″, 102C′ and102D′.

Afterwards, a mask element 402 is formed to cover the fin structures102C′ and 102D′ and the spacer elements 116′ surrounding the finstructures 102C′ and 102D′, as shown in FIG. 4B in accordance with someembodiments. The fin structures 102A″ and 102B″ and the spacer elements116′ surrounding the fin structures 102A″ and 102B″ are exposed withoutbeing covered by the mask element 402, as shown in FIG. 4B. The materialand formation method of the mask element 402 may be the same as orsimilar to those of the mask element 114 illustrated in FIG. 3D.

As shown in FIG. 4C, the spacer elements 116′ not covered by the maskelement 402 is partially removed, in accordance with some embodiments.As a result, spacer elements 121 which are shorter than the spacerelements 116′ are formed over the sidewalls of the fin structures 102A″and 102B″. In some embodiments, each of the spacer elements 121 isshorter than each of the spacer elements 116′. In some embodiments, anetching process is used to partially remove the spacer elements 116′ notcovered by the mask element 402 so as to form the spacer elements 121.The etching process may be an anisotropic etching process.

As shown in FIG. 4D, the fin structures 102A″ and 102B″ are partiallyremoved, in accordance with some embodiments. As a result, recessed (orthinned) fin structures 102C′ and 102D′ are formed. In some embodiments,an etching process is used to partially remove the fin structures 102A″and 102B″. The etchant used in the etching process may also partially orslightly remove the spacer elements 121. Therefore, spacer elements 121′that are lower than the spacer elements 121 are formed, as shown in FIG.4D in accordance with some embodiments. In some embodiments, recesses124 surrounded by the spacer elements 121′ are formed on the finstructures 102A′ and 102B′.

Many variations and/or modifications can be made to embodiments of thedisclosure. In some other embodiments, the spacer elements 121 arecompletely removed during or after the formation of the fin structures102A′ and 102B′. In these cases, the spacer elements 121′ are notformed.

As shown in FIG. 4E, the mask element 402 is removed, in accordance withsome embodiments. As a result, the fin structures 102A′, 102B′, 102C′and 102D′ and the spacer elements 121′ and 116′ are exposed. In someembodiments, each of the fin structures 102C′ and 102D′ is taller thaneach of the fin structures 102A′ and 102B′. The top surface of the finstructures 102C′ or 102D′ is higher than the top surfaces of the finstructures 102A′ and 102B′, as shown in FIG. 4E. In some embodiments,each of the spacer elements 116′ is taller than each of the spacerelements 121′.

Afterwards, one or more semiconductor materials are epitaxially grownover the fin structures 102A′, 102B′, 102C′, and 102D′, as shown in FIG.4E in accordance with some embodiments. Similar to the embodiments shownin FIG. 31, the merged semiconductor element 130 is formed on the finstructures 102A′ and 102B′. The isolated semiconductor elements 132 areformed on the fin structures 102C′ and 102D′, respectively. The mergedsemiconductor element 130 may serve as a source/drain structure of atransistor. The isolated semiconductor elements 132 which are separatedfrom each other by a distance may serve as source/drain structures ofdifferent transistors. Afterwards, similar to the embodimentsillustrated in FIG. 3J, surrounding portions 129A and 129B are formed,as shown in FIG. 4E in accordance with some embodiments.

Many variations and/or modifications can be made to embodiments of thedisclosure. In some other embodiments, the fin structures 102A, 102B,102C, and 102D are not in direct contact with the semiconductorsubstrate 100. FIG. 5 is a cross-sectional view of a semiconductordevice structure, in accordance with some embodiments. In someembodiments, the semiconductor substrate 100 is separated from the finstructures 102A, 102B, 102C, and 102D by an insulating layer 502. Theinsulating layer 502 may be made of or include silicon oxide, siliconnitride, silicon oxynitride, silicon carbide, one or more other suitablematerials, or a combination thereof. In these cases, the fin structures102A, 102B, 102C, and 102D may be formed by patterning a semiconductorlayer originally formed over the insulating layer 502.

As mentioned above, in some embodiments, the spacer elements 121′ arenot formed. FIG. 6 is a cross-sectional view of a semiconductor devicestructure, in accordance with some embodiments. As shown in FIG. 6, thespacer layer 112 over the sidewalls of the fin structures 102A′ and102B′ are completely removed. In these cases, the merged semiconductorelement 130 may extends from and be in direct contact with the isolationfeature 104, as shown in FIG. 6.

Embodiments of the disclosure form spacer elements with differentheights on sidewalls of different fin structures. Because the spacerelements have different heights, a subsequent epitaxial growth of asemiconductor material on the fin structures is confined in differentdegrees. As a result, a merged semiconductor element and a non-mergedsemiconductor element are formed in a single epitaxial growth process.Fabrication cost and time are significantly improved.

In accordance with some embodiments, a method for forming asemiconductor device structure us provided. The method includes forminga first fin structure, a second fin structure, and a third fin structureover a semiconductor substrate. The method also includes forming firstspacer elements over sidewalls of the first fin structure and sidewallsof the second fin structure. The method further includes partiallyremoving the first fin structure and the second fin structure after theformation of the first spacer elements. In addition, the method includesforming second spacer elements over sidewalls of the third finstructure, and each of the second spacer elements is taller than each ofthe first spacer elements. The method includes partially removing thethird fin structure after the formation of the second spacer elements.After the first fin structure, the second fin structure, and the thirdfin structure are partially removed, the method also includesepitaxially growing a semiconductor material over the first finstructure, the second fin structure, and the third fin structure. As aresult, a merged semiconductor element is formed on the first finstructure and the second fin structure, and an isolated semiconductorelement is formed on the third fin structure.

In accordance with some embodiments, a method for forming asemiconductor device structure us provided. The method includes forminga first fin structure, a second fin structure, and a third fin structureover a semiconductor substrate. The method also includes forming spacerelements over sidewalls of the third fin structure. The method furtherincludes recessing the third fin structure and recessing the first finstructure and the second fin structure such that top surfaces of thefirst fin structure and the second fin structure are lower than a topsurface of the third fin structure. In addition, the method includesepitaxially growing a semiconductor material over the first finstructure, the second fin structure, and the third fin structure afterthe first fin structure, the second fin structure, and the third finstructure are recessed. As a result, a merged semiconductor element isformed on the first fin structure and the second fin structure, and anisolated semiconductor element is formed on the third fin structure.

In accordance with some embodiments, a semiconductor device structure isprovided. The semiconductor device structure includes a first finstructure, a second fin structure, and a third fin structure over asemiconductor substrate. The semiconductor device structure alsoincludes first spacer elements over sidewalls of the first fin structureand sidewalls of the second fin structure. The semiconductor devicestructure further includes second spacer elements over sidewalls of thethird fin structure. Each of the second spacer elements is taller thaneach of the first spacer elements. In addition, the semiconductor devicestructure includes a merged semiconductor element on the first finstructure and the second fin structure. The semiconductor devicestructure also includes an isolated semiconductor element on the thirdfin structure.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for forming a semiconductor devicestructure, comprising: forming a first fin structure, a second finstructure, and a third fin structure over a semiconductor substrate;forming first spacer elements over sidewalls of the first fin structureand sidewalls of the second fin structure; partially removing the firstfin structure and the second fin structure after the formation of thefirst spacer elements; forming second spacer elements over sidewalls ofthe third fin structure, wherein each of the second spacer elements istaller than each of the first spacer elements; partially removing thethird fin structure after the formation of the second spacer elements;and after the first fin structure, the second fin structure, and thethird fin structure are partially removed, epitaxially growing asemiconductor material over the first fin structure, the second finstructure, and the third fin structure such that a merged semiconductorelement is formed on the first fin structure and the second finstructure, and an isolated semiconductor element is formed on the thirdfin structure.
 2. The method for forming a semiconductor devicestructure as claimed in claim 1, wherein forming the first spacerelements and the second spacer elements comprises: forming a spacerlayer over the first fin structure, the second fin structure, and thethird fin structure; removing a first portion of the spacer layer,wherein a first remaining portion of the spacer layer forms the firstspacer elements; and removing a second portion of the spacer layer,wherein a second remaining portion of the spacer layer forms the secondspacer elements.
 3. The method for forming a semiconductor devicestructure as claimed in claim 2, wherein forming the first spacerelements and the second spacer elements further comprises: forming afirst mask element to cover a first part of the spacer layer over thefirst fin structure and the second fin structure before removing thesecond portion of the spacer layer; removing the first mask elementafter the second spacer elements are formed; forming a second maskelement to cover the second spacer elements and the third fin structure;and removing the second mask element after the first spacer elements areformed.
 4. The method for forming a semiconductor device structure asclaimed in claim 1, wherein forming the first spacer elements and thesecond spacer elements comprises: forming a spacer layer over the firstfin structure, the second fin structure, and the third spacer layer;partially removing the spacer layer such that a first remaining portionof the spacer layer forms the second spacer elements, and a secondremaining portion of the spacer layer forms third spacer elements overthe sidewalls of the first fin structure and the second fin structure;forming a mask element to cover the second spacer elements and the thirdfin structure; and partially removing the third spacer elements afterthe mask element is formed, wherein a third remaining portion of thethird spacer elements form the first spacer elements.
 5. The method forforming a semiconductor device structure as claimed in claim 1, whereinthe second spacer elements are formed before the first spacer elements.6. The method for forming a semiconductor device structure as claimed inclaim 1, wherein epitaxially growing the semiconductor materialcomprises: using a first semiconductor-containing gas to epitaxiallygrow an inner portion of the merged semiconductor element and an innerportion of the semiconductor element; and using a secondsemiconductor-containing gas to epitaxially grow an outer portion of themerged semiconductor element and an outer portion of the semiconductorelement, wherein the second semiconductor-containing gas has a greaterdopant concentration than that of the first semiconductor-containinggas.
 7. The method for forming a semiconductor device structure asclaimed in claim 6, wherein the outer portion of the mergedsemiconductor element is larger than the outer portion of thesemiconductor element.
 8. The method for forming a semiconductor devicestructure as claimed in claim 1, wherein the merged semiconductorelement and the isolated semiconductor element are simultaneouslyformed.
 9. The method for forming a semiconductor device structure asclaimed in claim 1, further comprising forming an isolation feature tosurround lower portions of the first fin structure, the second finstructure, and the third fin structure, wherein: after partiallyremoving the first fin structure and the second fin structure, topsurfaces of the first fin structure and the second fin structure arebelow a top surface of the isolation feature, and after partiallyremoving the third fin structure, a top surface of the third finstructure is above the top surface of the isolation feature.
 10. Themethod for forming a semiconductor device structure as claimed in claim1, further comprising: forming a first gate stack partially covering thefirst fin structure and the second fin structure before the first spacerelements and the second spacer elements are formed; and forming a secondgate stack partially covering the third fin structure before the firstspacer elements and the second spacer elements are formed.
 11. A methodfor forming a semiconductor device structure, comprising: forming afirst fin structure, a second fin structure, and a third fin structureover a semiconductor substrate; forming spacer elements over sidewallsof the third fin structure; recessing the third fin structure; recessingthe first fin structure and the second fin structure such that topsurfaces of the first fin structure and the second fin structure arelower than a top surface of the third fin structure; and after the firstfin structure, the second fin structure, and the third fin structure arerecessed, epitaxially growing a semiconductor material over the firstfin structure, the second fin structure, and the third fin structuresuch that a merged semiconductor element is formed on the first finstructure and the second fin structure, and an isolated semiconductorelement is formed on the third fin structure.
 12. The method for forminga semiconductor device structure as claimed in claim 11, wherein formingthe spacer elements comprises: forming a spacer layer over the first finstructure, the second fin structure, and the third fin structure; andremoving a portion of the spacer layer over the sidewalls of the thirdfin structure such that a remaining portion of the spacer layer over thesidewalls of the third fin structure forms the spacer elements.
 13. Themethod for forming a semiconductor device structure as claimed in claim11, further comprising: forming a first mask element to cover a firstpart of the spacer layer over the first fin structure and the second finstructure; removing the first mask element after the spacer elements areformed; forming a second mask element to cover the spacer elements andthe third fin structure; removing at least a portion of the spacer layerover the sidewalls of the first fin structure and the second finstructure after the second mask element is formed; and removing thesecond mask element.
 14. The method for forming a semiconductor devicestructure as claimed in claim 13, wherein the spacer layer over thesidewalls of the first fin structure and the second fin structure arecompletely removed.
 15. The method for forming a semiconductor devicestructure as claimed in claim 11, wherein epitaxially growing thesemiconductor material comprises: using a first semiconductor-containinggas to epitaxially grow an inner portion of the merged semiconductorelement and an inner portion of the isolated semiconductor element; andusing a second semiconductor-containing gas to epitaxially grow an outerportion of the merged semiconductor element and an outer portion of theisolated semiconductor element, wherein the secondsemiconductor-containing gas has a greater dopant concentration thanthat of the first semiconductor-containing gas.
 16. A semiconductordevice structure, comprising: a semiconductor substrate; a first finstructure, a second fin structure, and a third fin structure over thesemiconductor substrate; first spacer elements over sidewalls of thefirst fin structure and sidewalls of the second fin structure; secondspacer elements over sidewalls of the third fin structure, wherein eachof the second spacer elements is taller than each of the first spacerelements; a merged semiconductor element on the first fin structure andthe second fin structure; and an isolated semiconductor element on thethird fin structure.
 17. The semiconductor device structure as claimedin claim 16, wherein the merged semiconductor element has a firstheight, the isolated semiconductor element has a second height, a ratioof the second height to the first height is in a range from about 0.7 toabout 0.9.
 18. The semiconductor device structure as claimed in claim16, wherein a top surface of the third fin structure is higher than atop surface of the first fin structure.
 19. The semiconductor devicestructure as claimed in claim 16, wherein: the isolated semiconductorelement comprises a first portion on the third fin structure and asecond portion surrounding the first portion, the second portion of theisolated semiconductor element has a greater dopant concentration thanthat of the first portion of the isolated semiconductor element, themerged semiconductor element comprises a third portion on the first finstructure, a fourth portion on the second fin structure, and a fifthportion surrounding the third portion and the fourth portion, and thefifth portion of the merged semiconductor element has a greater dopantconcentration than that of the third portion or that of the fourthportion of the merged semiconductor element.
 20. The semiconductordevice structure as claimed in claim 19, wherein the fifth portionoccupies a first fraction of the merged semiconductor element, thesecond portion occupies a second fraction ofthe isolated semiconductorelement, and the first fraction is greater than the second fraction.